1. Field of the Invention
The invention relates generally to the field of active pixel sensors, and more particularly to the architecture control circuits for active pixel sensors. More specifically, the invention relates to CMOS control circuits for active pixel sensors.
2. Description of the pior Art
Prior art active pixel sensors made from a CMOS process have used source/drain implants to form a photodiode, and polysilicon to form photogates as the light sensing elements. These light sensing elements have suffered from poor quantum efficiency, lag, and noise.
In order to overcome these problems, integration of a pinned photodiode in an active pixel sensor light sensing element was disclosed by Lee et al in U.S. Patent Application No. 08/421,173 to facilitate a pinned photo diode light sensing element within the architecture of an active pixel sensor. There is a shortcoming within this prior art device in that it does not show the manner in which the pixels are controlled by the control circuitry.
Prior art devices have numerous problems in integrating a camera system on a chip using CMOS process technology. These problems include column fixed pattern noise and the inability to fit the selection circuitry with the corresponding output amplifiers into a desired pixel pitch.
As can be seen by the foregoing discussion, there remains a need within the art for a method and apparatus of incorporating a pinned photodiode based image sensor within a CMOS device to alleviate fixed pattern noise, reduce the overall size of the device to achieve the desired pixel pitch, and to provide for a means to compensate for threshold voltage variation.